The present invention relates to the field of communication systems, and more particularly to an apparatus and method for high speed optical signal processing.
Various apparatus exist for performing attenuation, switching, add/drop multiplexing, phase shifting, mitigation of polarization mode dispersion, and various other signal processing functions. For example, micro-electro-mechanical systems (MEMS) have been developed, which implement moveable mirror structures that change position to affect a change in the optical signals being communicated. One such device implements the motion of alternate adjacent mirrors to create a grating effect that causes various levels of diffraction of the signals being processed. Depending on the level of signal diffraction, some signal processing functions, such as attenuation, can be performed. A problem with this approach, however, is that conventional diffraction-based solutions employing zeroth order reflection suffer from poor contrast ratios due to significant losses inherent in the operation of those devices.
Another MEMS approach involves using a movable mirror disposed outwardly from a substantially transmissive substrate to create a Fabry-Perot interference cavity between the two. These devices depend on multiple signal reflections within the interference cavity. As a result, small changes in signal wavelength can have a large impact on the operational characteristics of the device, resulting in a sharp spectral dependence. In addition, these devices typically require a tradeoff between device bandwidth and contrast ratio. As a result, these devices are generally incapable of offering both large bandwidth and good contrast ratios. Moreover, some of these devices operate at speeds too slow for particular signal processing operations. Others can be difficult to fabricate, rendering them too expensive for many applications.
The present invention recognizes a need for a method and apparatus operable to economically provide various optical signal processing functions, while maintaining high speed and good contrast ratios. In accordance with the present invention, an apparatus and method for providing high speed optical signal processing are provided that substantially reduce or eliminate at least some of the shortcomings associated with prior approaches.
In one aspect of the invention, an apparatus operable to facilitate optical signal processing comprises a micro-electro-optic system (MEMS) device including a moveable mirror layer operable to receive a first copy of an input signal from a beam splitter and to reflect the first copy of the input signal for combination with a second copy of the input signal at an output to form an output signal. The moveable mirror layer being displaceable in a substantially piston-like motion to introduce a phase shift between the first and second signal copies at the output. The amplitude of the output signal varying depending on the displacement of the moveable mirror layer.
In another aspect of the invention, a signal processing device comprises a beam splitter operable to receive an optical input signal and communicate at least two copies of the input signal in at least two directions. The device further comprises a plurality of reflective surfaces, each operable to receive one of the signal copies and to reflect the copies for ultimate combination at an output to form an output signal. At least one of the reflective surfaces comprises a moveable mirror layer of a first micro-electro-optic system (MEMS) device, the moveable mirror layer operable to experience a substantially piston-like motion to change its position relative to the first beam splitter, the change in position causing a phase shift between the signal copies and a corresponding interference between the signal copies at the output, the amplitude of the output signal operable to vary depending on the position of the moveable mirror.
In yet another aspect of the invention, a method of optical signal processing comprises receiving an optical input signal at an input and communicating a first copy of the input signal toward a first reflective surface and a second copy of the input signal toward second reflective surface, at least one of the reflective surfaces comprising a moveable mirror layer of a first micro-electro-optic system (MEMS) device. The method also includes reflecting the first and second signal copies toward an output and combining components of the reflected first and second signal copies to form at least one optical output signal. The method still further comprises displacing the moveable mirror layer in a substantially piston-like motion to result in an interference between the first and second signal copies at the output and a corresponding change in the amplitude of the output signal relative to the amplitude of the input signal.
Depending on the specific features implemented, particular embodiments of the present invention may exhibit some, none, or all of the following technical advantages. One aspect of the present invention provides highly reliable methods and apparatus capable of facilitating high speed optical signal processing at low costs. One aspect of the invention maintains high contrast ratios, while providing a device architecture that can be inexpensively produced, and reproduced to most any scale.
Various aspects of the invention provide advantages in terms of efficiency and speed of operation. For example, in one embodiment, the invention utilizes multiple moving mirrors to minimize the displacement required on any particular mirror. Still another option allows for mirrors located at grazing angles to the optical signals of less than forty-five degrees, which still further lessens the required mirror displacement needed to achieve a desired phase difference. By reducing each mirror""s necessary displacement, each of these options increases the efficiency of the invention by increasing the speed of the device, and reducing the drive voltage used to displace each mirror. Furthermore, any one or more of these and other features can be combined to further enhance the efficiency of the invention.
In one embodiment of the invention, a novel moveable mirror structure provides additional advantages in its efficiency of operation and ease of manufacture. Providing air gaps between a plurality of moveable mirror strips that move substantially in unison in response to a control signal facilitates control of air dampingxe2x80x94increasing the speed of the device and reducing the required drive voltage.
Various embodiments of the invention are easily scalable for use in a variety of multiple wavelength applications. Other technical advantages are readily apparent to one of skill in the art from the attached figures, description, and claims.